The drugs contain an active ingredient called zolpidem, which causes drowsiness. Researchers have found high levels of zolpidem in the blood of some patients the morning after a dose — so much so it affects patients’ cognitive skills, including their ability to drive.

The FDA said using lower doses of zolpidem will cut down on the amount of the drug found in the bloodstream the following morning. It also noted that the recommended dosage should be lower for women, because they don’t process zolpidem out of their system as quickly as men.

The agency recommended the dosage of zolpidem for women be lowered to 5 milligrams from 10 milligrams for immediate-release products and to 6.25 milligrams from 12.5 milligrams for extended-release products. Patients who use the extended-release forms of these drugs have an even higher risk for next morning impairment, according to the FDA.

The FDA said new labeling on the insomnia products will let doctors know they should consider a lower dose for men, especially for those who are having difficulty concentrating the next morning. And all patients, the FDA said, should be told about the possible “morning after” risks.

“Patients should also read the medication guides and understand the benefits and risks of these drugs,” said Dr. Ellis Unger of the FDA’s Center for Drug Evaluation and Research. “We believe that by lowering these doses, we can decrease the side effects that happen the morning after.”

Unger said that those who are taking these drugs talk to their doctors first before changing the dosage. He added that morning impairment is not limited to products with zolpidem. Drowsiness is a symptom listed on a number of insomnia drugs, and Unger said that alertness may be impaired even if the person doesn’t feel sleepy.

In making its recommendations, the FDA looked at findings from a large driving simulation study that showed some people taking products containing zolpidem had higher levels of the drug in their system and could not operate a vehicle as well as those who did not take the drugs, or who took lower doses.